Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of physical and media access control (MAC) specifications for implementing wireless local area network (WLAN) communications. These specifications provide the basis for wireless network products using the Wi-Fi brand managed and defined by the Wi-Fi Alliance. The specifications define the use of the 2.400-2.500 GHz as well as the 4.915-5.825 GHz bands. These spectrum bands are commonly referred to as the 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channels with a center frequency and bandwidth. The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, though some countries regulate the availability of these channels. The 5 GHz band is more heavily regulated than the 2.4 GHz band and the spacing of channels varies across the spectrum with a minimum of a 5 MHz spacing dependent on the regulations of the respective country or territory.
IEEE 802.11 based WLAN systems rely on Clear-Channel-Assessment (CCA), in the physical layer (PHY) that determines the current state of use of the wireless medium (WM), such that a station will access a given wireless channel only when the WM becomes idle (i.e. there is no transmission on the wireless medium and other qualifying conditions are met). Some CCA rule mechanisms, for example some of the rule mechanisms defined in IEEE 802.11, indicate that the primary channel is Busy, if one of the conditions listed in Table I is met, otherwise the primary channel is determined to be Idle. If the primary channel is idle, then the PHY layer will check the secondary channels.
TABLE IOperating Channel WidthConditions20 MHz, 40 MHz, 80 MHz, The start of a 20 MHz NON_HT PPDU in the160 MHz or 80 + 80 MHzprimary 20 MHz channel as defined in18.3.10.6 (CCA requirements)40 MHz, 80 MHz, 160The start of a 40 MHz non-HT duplicate orMHz or 80 + 80 MHzVHT PPDU in the primary 40 MHz channel at or above −79 dBm,The start of an HT PPDU under theconditions defined in 20.3.21.5 (CCAsensitivity)80 MHz, 160 MHz or The start of an 80 MHz non-HT duplicate or80 + 80 MHzVHT PPDU in the primary 80 MHz channelat or above −76 dBm60 MHz or 80 + 80 MHzThe start of a 160 MHz or 80 + 80 MHz non-HT duplicate or VHT PPDU at or above −73dBm